/// From https://github.com/night-shift/fpconv
/// Boost Software License 1.0
/// See accompanying license file

#pragma once

#include <stdint.h>

#define npowers 87
#define steppowers 8
#define firstpower -348 /* 10 ^ -348 */

#define expmax -32
#define expmin -60

typedef struct Fp {
   uint64_t frac;
   int      exp;
} Fp;

static Fp powers_ten[] = {
   { 18054884314459144840U, -1220 }, { 13451937075301367670U, -1193 }, { 10022474136428063862U, -1166 },
   { 14934650266808366570U, -1140 }, { 11127181549972568877U, -1113 }, { 16580792590934885855U, -1087 },
   { 12353653155963782858U, -1060 }, { 18408377700990114895U, -1034 }, { 13715310171984221708U, -1007 },
   { 10218702384817765436U, -980 },  { 15227053142812498563U, -954 },  { 11345038669416679861U, -927 },
   { 16905424996341287883U, -901 },  { 12595523146049147757U, -874 },  { 9384396036005875287U, -847 },
   { 13983839803942852151U, -821 },  { 10418772551374772303U, -794 },  { 15525180923007089351U, -768 },
   { 11567161174868858868U, -741 },  { 17236413322193710309U, -715 },  { 12842128665889583758U, -688 },
   { 9568131466127621947U, -661 },   { 14257626930069360058U, -635 },  { 10622759856335341974U, -608 },
   { 15829145694278690180U, -582 },  { 11793632577567316726U, -555 },  { 17573882009934360870U, -529 },
   { 13093562431584567480U, -502 },  { 9755464219737475723U, -475 },   { 14536774485912137811U, -449 },
   { 10830740992659433045U, -422 },  { 16139061738043178685U, -396 },  { 12024538023802026127U, -369 },
   { 17917957937422433684U, -343 },  { 13349918974505688015U, -316 },  { 9946464728195732843U, -289 },
   { 14821387422376473014U, -263 },  { 11042794154864902060U, -236 },  { 16455045573212060422U, -210 },
   { 12259964326927110867U, -183 },  { 18268770466636286478U, -157 },  { 13611294676837538539U, -130 },
   { 10141204801825835212U, -103 },  { 15111572745182864684U, -77 },   { 11258999068426240000U, -50 },
   { 16777216000000000000U, -24 },   { 12500000000000000000U, 3 },     { 9313225746154785156U, 30 },
   { 13877787807814456755U, 56 },    { 10339757656912845936U, 83 },    { 15407439555097886824U, 109 },
   { 11479437019748901445U, 136 },   { 17105694144590052135U, 162 },   { 12744735289059618216U, 189 },
   { 9495567745759798747U, 216 },    { 14149498560666738074U, 242 },   { 10542197943230523224U, 269 },
   { 15709099088952724970U, 295 },   { 11704190886730495818U, 322 },   { 17440603504673385349U, 348 },
   { 12994262207056124023U, 375 },   { 9681479787123295682U, 402 },    { 14426529090290212157U, 428 },
   { 10748601772107342003U, 455 },   { 16016664761464807395U, 481 },   { 11933345169920330789U, 508 },
   { 17782069995880619868U, 534 },   { 13248674568444952270U, 561 },   { 9871031767461413346U, 588 },
   { 14708983551653345445U, 614 },   { 10959046745042015199U, 641 },   { 16330252207878254650U, 667 },
   { 12166986024289022870U, 694 },   { 18130221999122236476U, 720 },   { 13508068024458167312U, 747 },
   { 10064294952495520794U, 774 },   { 14996968138956309548U, 800 },   { 11173611982879273257U, 827 },
   { 16649979327439178909U, 853 },   { 12405201291620119593U, 880 },   { 9242595204427927429U, 907 },
   { 13772540099066387757U, 933 },   { 10261342003245940623U, 960 },   { 15290591125556738113U, 986 },
   { 11392378155556871081U, 1013 },  { 16975966327722178521U, 1039 },  { 12648080533535911531U, 1066 }
};

static Fp find_cachedpow10(int exp, int* k) {
   const double one_log_ten = 0.30102999566398114;

   int approx = -(exp + npowers) * one_log_ten;
   int idx    = (approx - firstpower) / steppowers;

   while (1) {
      int current = exp + powers_ten[idx].exp + 64;

      if (current < expmin) {
         idx++;
         continue;
      }

      if (current > expmax) {
         idx--;
         continue;
      }

      *k = (firstpower + idx * steppowers);

      return powers_ten[idx];
   }
}